1. Field of Invention
The present invention relates to a power-saving control circuit for an OLED (organic light emitting diode) panel, and a method thereof. In particular, the present invention relates to a control circuit and a method which adaptively adjusts the supply voltage of OLEDs so that the power consumption of the OLED panel is effectively controlled.
2. Description of Related Art
FIG. 1 is a schematic circuit diagram showing a typical structure of a conventional passive OLED panel control circuit 10. As shown in the figure, the circuit 10 includes n organic LEDs OLED1-OLEDn, respectively located in paths 11-1n. The conduction of each of the paths 11-1n is controlled by a corresponding signal RS1-RSn; in a passive OLED panel, each path is conducted in turn so that the panel shows an image as a whole (by residual vision of human eyes). The brightness of each of the organic LEDs OLED1-OLEDn is controlled by the current amount on the corresponding path 11-1n, which is controlled by a corresponding digital to analog converter (DAC) DAC1-DACn. For simplicity of the figure, each DAC is only connected with one OLED, but it may be connected with more than one OLED in a real case. Each digital to analog converter DAC1-DACn may be of a relatively simple structure as shown in FIG. 2, or of a cascoded type structure as shown in FIG. 3.
More specifically, the brightness of each of the organic LEDs OLED1-OLEDn is controlled as follows. The transistor Q and a transistor in each of the digital to analog converters DAC1-DACn forms a current mirror, which mirrors the current of the current source CS proportionally to each of the digital to analog converters DAC1-DACn. A digital control signal SW, also referred to as the column signal, or segment signal, determines which transistors in the DAC are conducted. As an example, the current amount flowing through the transistors shown in FIG. 2 may respectively be 1×, 2×, 4×, and 8×, so that a 16-level brightness variation may be generated according to the digital control signal SW.
For an OLED panel, power consumption and heat dissipation have been the primary concerns. In the abovementioned prior art, to assure that each of the organic LEDs OLED1-OLEDn functions normally, usually a designer tends to design the value of the supply voltage Vcc in a conservative way (that is, to assign a higher value than necessary to assure the brightness of the OLEDs). Therefore, the human-assigned value of Vcc is often not optimum (not the minimum required voltage). This inevitably causes unnecessary power consumption and increases heat.